To meet the demand for wireless data traffic, which has increased since deployment of 4th-generation (4G) communication systems, efforts have been made to develop an improved 5th-generation (5G) or pre-5G communication system. Therefore, the 5G or pre-5G communication system is also called a ‘beyond 4G network’ or a ‘post long-term evolution (LTE) system’.
It is considered that the 5G communication system will be implemented in millimeter wave (mmWave) bands, e.g., 60 GHz bands, so as to accomplish higher data rates. To reduce propagation loss of radio waves and increase a transmission distance, a beam forming technique, a massive multiple-input multiple-output (MIMO) technique, a full dimensional MIMO (FD-MIMO) technique, an array antenna technique, an analog beam forming technique, and a large scale antenna technique are discussed in 5G communication systems.
In addition, in 5G communication systems, development for system network improvement is under way based on advanced small cells, cloud radio access networks (RANs), ultra-dense networks, a device-to-device (D2D) communication, a wireless backhaul, a moving network, a cooperative communication, coordinated multi-points (CoMP), reception-end interference cancellation, and the like.
In the 5G system, a hybrid frequency shift keying (FSK) and quadrature amplitude modulation (QAM) modulation (FQAM) and a sliding window superposition coding (SWSC) as an advanced coding modulation (ACM) scheme, and a filter bank multi carrier (FBMC) scheme, a non-orthogonal multiple access (NOMA) scheme, and a sparse code multiple access (SCMA) scheme as an advanced access technology have been developed.
Various schemes for increasing system throughput have been proposed, and a typical one is a MIMO scheme using a plurality of antennas. In the MIMO scheme, it is essential for a transmitter to acquire accurate channel state information (CSI) in order to use signal processing techniques which enable high data rate transmission.
In cellular systems supporting a frequency division duplexing (FDD) scheme, CSI estimated in a receiver is transmitted to a transmitter through a feedback link.
In a massive MIMO scheme including a plurality of antennas, there is a need for a plurality of feedback bits for accurately quantizing CSI.
Here, a normalized beamforming gain using a random vector quantization (RVQ) codebook may be expressed in Equation 1.
                    G        ⁢                  =          .                ⁢                              E            ⁡                          [                              |                                                                            h                      H                                                              ||                      h                      ⁢                                              ||                        2                                                                              ⁢                  c                                ⁢                                  |                  2                                            ]                                ≈                      1            -                          2                              -                                  B                                      M                    -                    1                                                                                                          Equation        ⁢                                  ⁢        1            
In Equation 1, h∈M denotes a multiple input single output (MISO) channel vector, C∈M denotes a unit norm beamforming codeword, B denotes the number of feedback bits for an RVQ codebook, and M denotes the number of antennas.
A feedback overhead according to the number of general massive MIMO antennas will be described with reference to FIG. 1.
FIG. 1 schematically illustrates a feedback overhead according to the number of general massive MIMO antennas according to the related art.
Referring to FIG. 1, a vertical axis indicates the number of transmission (Tx) antennas, and a horizontal axis indicates the number of bits required for feedback. It will be noted that curves indicating feedback overheads according to the number of massive MIMO antennas in FIG. 1 are curves indicating feedback overheads according to the number of massive MIMO antennas in a case that target gains are 0.5, 0.6, 0.7, and 0.8. Here, a target gain is Gtarget.
As shown in FIG. 1, it will be understood that a feedback overhead increases proportional to the number of antennas. This massive feedback overhead acts as significant load to feedback links.
So, there is a need for a scheme of performing a beamforming operation thereby decreasing feedback overhead in a communication system supporting an FD-MIMO scheme.
The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present disclosure.